1. Field of the Invention
The present invention relates generally to a method of and apparatus for generating high-resolution bilevel image data, and more particularly, to a method of and apparatus for scanning bilevel originals (e.g., black-and-white originals) and processing multi-gradation image data to generate bilevel image data which are higher in resolution than the inputted multi-gradation image data.
2. Description of the Prior Art
In an image scanning/recording device, input image data obtained by scanning an original are limited in resolution due to technical or economic considerations. For example, a typical commercially available CCD imagescanner for reading has an upper limit of a scanning line number of 400 lines/inch (input resolution of 63.5 .mu.m square) in the existing circumstances, and such resolution is sufficient in practice.
In the field of commercial printing and publishing printing requiring high quality, on the other hand, it is said that resolution preferably exceeds an output scanning line number of at least 1500 lines/inch (16.9 .mu.m square) so that no jagged portion is defined on the edges of an image developed by bilevel image processing device that scans a bilevel image, performs image processing on it and outputs the image in full-size magnification. Such high resolution is required also in the input area on the premise of full-size processing. However, a bilevel image input device capable of reading an image with a resolution exceeding 1500 lines/inch is considerably more expensive.